The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Meeting the present demands of increased power density and higher efficiency can be difficult in power converters having high output requirements. Various techniques have been developed in an attempt to satisfy these two demands. Such techniques include using multiple circuit elements such as multiple power switches, diodes, and chokes for better thermal management and higher efficiency.
FIG. 1 illustrates a boost converter 100 including some of the techniques described above. The boost converter 100 includes an alternating current (AC) power source 101, output terminals 102, 103, an output capacitor C2, power switches Q1 and Q2, boost diodes D6 and D7 and boost chokes L1, L2 and L3. The boost choke L3 is a coupled split boost choke having windings L31 and L32. The winding L31 and the boost diode D6 form a first power rail 104 and the winding L32 and the boost diode D7 form a second power rail 106. Also shown in FIG. 1 is a load R3 connected to the output terminals 102, 103. The load R3 can be, for example, a power converter requiring a PFC front end circuit.
Generally, during operation of the boost converter 100, energy is stored in the boost chokes L1, L2 and L3 when the power switches Q1 and Q2 are closed. When the power switches Q1 and Q2 are opened, the boost diodes D6 and D7 become forward biased and the energy stored in the boost chokes L1, L2 and L3 flows through the power rails 104 and 106 to the output terminal 102.
Using a coupled split boost choke, such as the coupled split boost choke L3, is one known technique to balance the currents flowing in the power rails 104 and 106. As recognized by the inventors, however, the currents flowing in the power rails 104 and 106 can remain unbalanced even though windings L31 and L32 are coupled. Such unbalanced currents can be caused by various factors including differences between the forward voltage drops of the boost diodes D6 and D7, the leakage inductance between the split choke windings L31 and L32, the trace inductance between the anode of the boost diode D6 and the winding L31, the trace inductance between the anode of the boost diode D7 and the winding L32, the branch inductance between the windings L31 and L32 and the power switches Q1 and Q2, and/or mismatches between the power switches Q1 and Q2 with respect to output capacitance, gate voltage, threshold voltage and/or gate drivers, and possibly other factors.
As a result of the current flow imbalance, the boost diodes D6 and D7 and the power switches Q1 and Q2 are typically overrated by about 130% to 150%. However, failures during operation of the boost converter 100 can still be expected even if the boost diodes D6 and D7 and the power switches Q1 and Q2 are overrated. For example, the boost converter 100 could fail during step load or input line transient conditions. Furthermore, the thermal performance of the power rails 104 and 106 can be unstable in the absence of overrated and/or expensive heat sinks.